"It sounded like a canon or something. It was loud. We turned around, and it was a huge cloud of smoke, and then saw another one, and then every body was like, 'Oh my gosh, what do we do?'" Algiers said.

Lisa Martin, of Glendale, said she and her husband were inside a warming tent beyond the finish line when police came rushing in.

"All of a sudden, the cops came up to us and, 'It's a bomb, you have to go. You have to go, there are bombs.' It was like a whirlwind," Martin said.

Sean McBride, of Mequon, said he crossed the spot of the blast not long before the explosions.

"To know I was there just a half hour before that occurred was really a shock. One of the most difficult things I've ever had to go through personally, emotionally," he said.